1. Field of the Invention
The present invention relates to a method and apparatus for avoiding mutual interference between wireless communication systems, and more particularly, to an improved method and apparatus for avoiding mutual interference between wireless communication systems by deciding data transmission according to a state of a communication channel. The present application is based on Korean Application No. 2001-26019, filed on May 12, 2001, which is incorporated herein by reference.
2. Description of the Related Art
Recently, a wireless data communication system is designed to exclusively use a certain frequency band. That is to say, it is not considered that a variety of systems using an identical frequency band coexist in some environments at the same time, as shown in FIG. 1. However, in the case of a frequency band usable without permission of the government, various systems can coexist in the identical frequency band. For example, a wireless LAN, Bluetooth, home RF, medical instrument and microwave oven coexist in an industrial scientific medical (ISM) band of 2.4 GHz. Since a plurality of systems coexist in a restricted frequency band, transmission/reception modulation frequencies are inevitably overlapped.
In the case that the modulation frequencies are overlapped, the systems cannot normally perform communication due to mutual interference, and performance thereof is deteriorated. One system recognizes the signals from the other systems using the identical frequency band as noise due to the mutual interference, and thus cannot normally perform the communication.
FIG. 2 shows mutual interference between an IEEE 802.11b network (hereinafter, referred to as “wireless LAN”) and a Bluetooth system which both use the identical frequency of 2.4 GHz band. Referring to FIG. 2, one high rate wireless LAN data packet modulated in a direct sequence spread spectrum (DSSS) of 1500 bytes collides with two Bluetooth data slots. Accordingly, the packet colliding with the data of a different system is difficult to be normally demodulated in a reception terminal. Likewise, the data of the system is rarely normally demodulated.
FIG. 3 shows mutual interference between the wireless LAN system and the Bluetooth systems composing a multi-Piconet, each system employing the identical frequency of 2.4 GHz band. As shown therein, a collision takes place in a frequency ƒ3 due to interference between Bluetooth multi-Piconets and in a frequency ƒ21 due to interference between a Bluetooth system and the wireless LAN system.
FIG. 4 shows variations of a data throughput of the wireless LAN system in a state where the wireless LAN system and the Bluetooth system coexist, which has been disclosed in a treatise by Jim Zyren (Bluetooth '99, June 1999). In the case that a packet payload is 1500 bytes in the wireless LAN system, when the Bluetooth system is not operated, namely the wireless LAN system merely exists, the throughput is over 7 Mbps. However, when the Bluetooth terminal has a load of 100% to transmit an E-mail, the throughput of the wireless LAN system is reduced by half, to about 3.5 Mbps.
Therefore, there are increasing demands for a method for avoiding interference and data collision in the communication system. For this, a variety of methods have been suggested.
The wireless LAN system currently uses a carrier sense multiple access with collision avoidance (CSMA/CA) to avoid data collision. A transmission terminal transmits a transmission intention signal before transmitting data, and transmits the data when receiving a response from a reception terminal, thereby avoiding collision with data from a different transmission terminal. However, the CSMA/CA serves to prevent data collision in a single system, and thus is not suitable to avoid collision between different systems.
The CSMA/CA always transmits a collision confirmation signal before data transmission in order to avoid a transmission collision between the terminals. Consequently, network traffic is increased due to the transmission intention signal, thus reducing network speed. In addition, when a terminal which is not sensed by the transmission terminal transmits/receives data to/from the reception terminal, the transmission terminal consecutively transmits the transmission intention signal, which results in reduced performance of the CSMA/CA.
To solve the foregoing problems, the Mobilian corporation has taught a method for monitoring and controlling data transmission of a wireless LAN system and a Bluetooth system by using a MAC Enhanced Temporal Algorithm (MEHTA) engine, as shown in FIG. 5. When the MEHTA engine is specially installed, interference between an adaptive frequency hopping (AFH) type Bluetooth system and a direct spread type wireless LAN is efficiently prevented. However, the MEHTA engine cannot be applied to interference by a frequency spread type wireless LAN and a different Bluetooth Piconet. Especially, the Bluetooth protocol may be widely utilized for a notebook computer and a wireless telephone, but the MEHTA engine is not applied to interference by the different Bluetooth Piconet.